1. Field of the Invention
The present invention relates to electrophotographic apparatus for use in, for example, copying machines, printers, electrostatic recording, facsimile, and electrostatic printing.
2. Description of the Related Art
The present invention relates to image-fixing apparatus for use in electrophotographic image forming apparatus used in, for example, copying, facsimile, and printing.
In image-fixing procedures of electrophotographic image forming apparatus, image-fixing members such as belts and rollers are exposed to repeated temperatures changes within wide ranges from room temperature to high temperatures and to pressure of great forces. Such belts for use in image-fixing must have satisfactory heat resistance and mechanical strength that can endure these harsh environments. In conventional image-fixing apparatuses, a recording medium is pressurized and nipped through a heating medium such as a heating roller or heating endless belt. Thus, a toner on the roller or endless belt is heated, melted and pressurized to thereby yield a toner image fixed on the recording medium. Concurrently with this image-fixing procedure, the toner develops adhesion to the heating medium. To release the recording medium bearing the toner from the heating medium, a mold-releasing layer of a fluororesin such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkylvinyl ether copolymers (PFA) and fluorinated ethylene propylene copolymers (FEP) is formed on a surface of the heating member such as a heating roller or heating endless belt. In addition, to release the pressurizing medium from the backside of the recording medium, another mold-releasing layer of a fluororesin such as PTFE, PFA or FEP is formed on a surface of the pressurizing medium such as a pressurizing roller or pressurizing endless belt arranged on the opposite side of the heating member. However, these fluorine-containing resins lead slip among molecules, and the mold-releasing layer wears at a high speed during a long-term use and thereby has a short life. Accordingly, a demand has been made on solving the wear resistance problems.
As a possible solution to these problems, Japanese Patent (JP-B) No. 2984409, JP-B No. 2984404, and JP-B No. 3261166 describe that the wear resistance is improved by using a polybenzimidazole on a surface of the roller. In fact, such polybenzimidazoles have very high heat resistance and mechanical strength and very excellent wear resistance. However, when the surface layer of these mediums is made from a polybenzimidazole, the surface layer will have insufficient mold releasability, although it invites less abrasion due to its increased mechanical strength. In other words, such members for use in toner image-fixing in electrophotographic image forming apparatus must have not only high wear resistance but also satisfactory mold releasability for stably releasing the recording medium without attachment of the molten toner to an image-fixing plane. If a layer of a fluororesin such as PTFE, PFA or FEP is formed on the surface layer to exhibit excellent mold releasability, the resulting surface layer will have insufficient wear resistance. Accordingly, increasing demands have been made on techniques that can improve wear resistance while maintaining satisfactory mold releasability.
Certain heat-resistant polyimide silicone resins have been known. Examples of such resins are PIX series (trade name, available from Hitachi Chemical Co., Ltd.), KJR series (trade name, available from Shin-Etsu Chemical Co., Ltd.) and BE series (trade name, available from Bergston and Associates). The PIX series products have a viscosity of 1.1 Pa·s at 25° C. and a weight loss starting temperature of 450° C. The KJR series products have a viscosity of 1.4 Pa·s to 2.6 Pa·s at 25° C. and a weight loss starting temperature of 440° C. However, these heat-resistant polyimide silicone resins have been used for improving adhesion of SiO2 films on substrate wafers at high humidity in manufacturing of semiconductors (“Silicone Handbook” pp. 501-503, Aug. 31, 1990, The Nikkan Kogyo Shimbun) and there is no suggestion for using these heat-resistant polyimide silicone reins for improving wear resistance in electrophotographic toner image-fixing apparatuses.